pg_dump -s -b
All,
While reviewing and considering the patch to add the --no-blobs option
to pg_dump, which I entirely agree with, I came across our claim that
passing -b to pg_dump would cause blobs to be output, regardless of
other options set.
To wit, our docs specifically say:
----
Include large objects in the dump. This is the default behavior except
when --schema, --table, or --schema-only is specified, so the -b switch
is only useful to add large objects to selective dumps.
----
However, a 'pg_dump -s -b' won't include blobs, which appears to be due
to the masking performed in _tocEntryRequired() whereby we strip the
REQ_DATA out if we are in schema-only mode.
Further, though perhaps less surprising, we don't include blobs when
--section=post-data is set, and only the definition of the blob (but no
data) when --section=pre-data is used.
This appears to go back at least as far as all currently supported
branches.
We have a few options here. The documentation says 'selective dumps',
which we could infer to mean 'dumps where the user specified a table' or
similar and exclude 'schema-only' from that case. I don't believe this
was the original intent, given this comment in pg_dump.c:
/*
* Dumping blobs is now default unless we saw an inclusion switch or -s
* ... but even if we did see one of these, -b turns it back on.
*/
Given the lack of field complaints about this, I'm pretty tempted to
just adjust that comment and the documentation. Alternativly, we could
hack things up in a simimlar manner to what was done in a7e5457, and
cause blobs to be dumped even in schema-only mode if -b is passed.
Thoughts?
Thanks!
Stephen
Stephen Frost <sfrost@snowman.net> writes:
To wit, our docs specifically say:
----
Include large objects in the dump. This is the default behavior except
when --schema, --table, or --schema-only is specified, so the -b switch
is only useful to add large objects to selective dumps.
----
Clearly, this is an oversimplification.
However, a 'pg_dump -s -b' won't include blobs, which appears to be due
to the masking performed in _tocEntryRequired() whereby we strip the
REQ_DATA out if we are in schema-only mode.
Further, though perhaps less surprising, we don't include blobs when
--section=post-data is set, and only the definition of the blob (but no
data) when --section=pre-data is used.
IMO, blobs are data, so those behaviors are correct. The docs should
be fixed to match the code.
regards, tom lane
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
* Tom Lane (tgl@sss.pgh.pa.us) wrote:
IMO, blobs are data, so those behaviors are correct. The docs should
be fixed to match the code.
Works for me.
Thoughts on the attached?
Thanks!
Stephen
Attachments:
pg_dump_blobs_doc_fix.patchtext/x-diff; charset=us-asciiDownload
diff --git a/doc/src/sgml/ref/pg_dump.sgml b/doc/src/sgml/ref/pg_dump.sgml
new file mode 100644
index 371a614..04b3124
*** a/doc/src/sgml/ref/pg_dump.sgml
--- b/doc/src/sgml/ref/pg_dump.sgml
*************** PostgreSQL documentation
*** 138,145 ****
<para>
Include large objects in the dump. This is the default behavior
except when <option>--schema</>, <option>--table</>, or
! <option>--schema-only</> is specified, so the <option>-b</>
! switch is only useful to add large objects to selective dumps.
</para>
</listitem>
</varlistentry>
--- 138,148 ----
<para>
Include large objects in the dump. This is the default behavior
except when <option>--schema</>, <option>--table</>, or
! <option>--schema-only</> is specified. The <option>-b</>
! switch is therefore only useful to add large objects to dumps
! where a specific schema or table has been requested. Note that
! blobs are considered data and therefore will be included when
! --data-only is used, but not when --schema-only is.
</para>
</listitem>
</varlistentry>